Vacuum ultraviolet (VUV) light sources are attractive for processing optical materials since the high photon energy of such sources permits photochemical bond breaking. This property, plus the relatively short pulse characteristics of these sources, open a variety of semiconductor and flat panel display processing applications. These applications include photo-resist ashing, metal planarization, annealing of amorphous silicon devices to polysilicon devices, such as liquid crystal displays and silicon on insulators, and activation of electroluminescent phosphors. Currently, in the case of annealing, processing is achieved using lasers, the output of which are rastered over the surface to be treated.
Deposition of high energy into a narrow-width surface discharge has been shown to generate copious quantities of ultraviolet radiation by A. S. Bashkin et al. in "High-Power 1 .mu.sec Ultraviolet Radiation Source For Pumping Of Gas Lasers," Sov. J. Quantum Electron. 6, 994-996 (1976). Stored electrical energy as high as 50 kJ was available for pumping gas lasers. Efficient production of ultraviolet radiation from the surface of a dielectric material has also been studied by R. E. Beverly, III et al. in "Ultraviolet Spectral Efficiencies Of Surface-Spark Discharges With Emphasis On The Iodine Photodissociation Laser Pumpband," Appl. Optics 16, 1572-1577 (1977). Electrical conversion efficiencies into the 250-290 nm band of the electromagnetic spectrum were reported to be 4.5% for the optical pumping of the iodine photodissociation laser. Various ceramic dielectric materials and buffer gases were employed in order to characterize the desired ultraviolet radiation output, since it was observed that the output intensity in a given spectral region was strongly dependent upon these parameters. The measurements were performed at relatively low energy (approximately 20 Joules), and little care was taken to insure uniformity of the discharge.
For many semiconductor and flat panel display processing applications, a uniform, large surface area light source is required. Previous research by the present inventors into large-area surface discharges (5 cm.times.20 cm) for pumping chemical lasers, used a grounded back plane and a Teflon dielectric plate, and generated a ribbon-like plasma having multiple streamers at stored electrical energies of 1.7 kJ. However, in order to use such ultraviolet sources for processing semiconductor materials, fluoro- and chlorocarbons cannot be present since under intense ultraviolet radiation, carbon particles are formed. This is an unacceptable contamination for any semiconductor processing applications. It is also known that large-area dielectric materials are too brittle to withstand the repeated shocks generated by the 2-4 kJ energy pulses desired to be deposited into the surface discharge.
Accordingly, it is an object of the present invention to provide an ultraviolet light source uniform over a large area which is suitable for processing contamination-sensitive materials, and which does not generate significant quantities of ions which may damage the materials.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.